1. Field of the Invention
The invention relates to a phosphor (fluorescent substance) that is efficiently excited by ultraviolet rays or in a short-wavelength region to emit light.
2. Description of the Related Art
A variety of light-emitting devices are known, which are configured to produce light of the desired color by using a combination of a light-emitting element and a phosphor that is excited by light emitted from the light-emitting element so as to produce light in a wavelength region different from that of the light-emitting element.
In recent years, white light-emitting device modules with long life and low power consumption have drawn attention, which are configured to produce white light by using a combination of a semiconductor light-emitting element such as a light-emitting diode (LED) or a laser diode (LD) that emits ultraviolet light or short-wavelength visible light and a phosphor that uses the light-emitting element as an excitation light source.
Known examples of such white light-emitting modules include systems using a combination of an LED that emits ultraviolet rays or short-wavelength visible light and different phosphors that are excited by ultraviolet rays or short-wavelength visible light to emit light beams of colors such as blue and yellow, respectively.
A yellow phosphor described in JP 2009-38348 includes a halogen element. Therefore, a metal halide such as SrCl2, CaCl2, or the like is used as a source of a halogen element for a material used for the preparation of a phosphor.
However, SrCl2 and CaCl2 are high in absorbency and require careful attention when SrCl2 and CaCl2 are treated in the atmosphere. In other words, if SrCl2 or CaCl2 is mixed with another material as a raw material of a phosphor in the atmosphere, the amount of moisture content may greatly change depending on the humidity, and the composition of the phosphor that is prepared may not be stable. As a result, it is necessary to devise equipment or steps in order to maintain the properties of the phosphor.